The embodiment relates to a phosphor and a light emitting device having the same. The light emitting device may be included in a lighting system.
A LED (Light Emitting Device) is a device having a property of converting electrical energy into light energy. For example, the LED may represent various colors by adjusting the compositional ratio of compound semiconductors.
For instance, a nitride semiconductor represents superior thermal stability and wide bandgap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been commercialized and extensively used.
A LED of emitting white color light, which employs a secondary light source of emitting light by coating phosphor, is generally implemented through a scheme of coating YAG:Ce phosphor of generating yellow color light on a blue LED.
However, according to the scheme described above, due to quantum deficits and reradiation efficiency caused by secondary light, the efficiency is degraded and the color rendering is not easy.
Thus, since a white LED backlight according to the related art has the combination of a blue LED and a yellow phosphor, the white LED backlight lacks of green and red components, so that colors are unnaturally represented. For this reason, the white LED backlight has been limitedly applied to a display of a cellular phone or a laptop computer. Nevertheless, the white LED backlight according to the related art has been extensively used because the white LED backlight is easily driven and remarkably inexpensive.
Generally, it is well known in the art that the phosphor material may include a silicate, a phosphate, an aluminate, or a sulfide and a transition metal or a rare earth metal is used at the center of light emission. For example, although silicate phosphor has been used for a backlight unit or a lighting device, the silicate phosphor is weak to moisture so the reliability of the silicate phosphor is inferior to any other phosphors.
Meanwhile, although a phosphor for a white LED, which is excited by an excitation source having high energy such as ultraviolet light or blue light to emit visible light, has been mainly developed, if the phosphor according to the related art is exposed to the excitation source, the luminance of the phosphor is reduced.